Light wt. engine lid

[Randy Webb]

Is it possible to get a good fit from a carbon fiber or fiberglass rear deck lid (engine lid)? I'd like to lose a little wt. back there and found an Al one for sale (4 lbs.), but the cost is $700(!).
This is the regular lid -- no ducktail.

Any experiences? And if you got a fit equal to or better than stock, where did you buy the lid? Thanks.

[Bill Verburg]

f/g will be less stable than carbon fiber. But accepable if not perfect results can be obtained w/ either. The fact that there won't be a tail makes it more difficult because that large relatively flat surface will show any warping or misalignment more easily than a tail where the spoiler blocks sight lines.

I would go w/ carbon fiber or the expensive al. tail if it were my car.

Did you see that Peter @ Rennspeed now has at least 1 al. licence plate panel for only $75 sounds like a great light weight addition for an early car on a diet.




Al. licence panel

[Randy Webb]

Huh - that's interesting -- I wonder how much st. it saves?

Thx for the info on the lids. - Randy

[Bill Verburg]

I've got 2 lids hanging around which I just weiged on a bathroom scale (it agrees w/ my docs office scale so it can't be off by too much though these measurements are very suspect once out of the design range of the scale) both are stripped of all hardware one is from a '72 and one from an '82 they both come in a tad under 10#s say 9#s? ea. so somewhere less than that is the potential savings.

I apologize for not responding when you posed that ? over on Rennlist but it was just too d*** cold that night.

[lateapex911]

PAR has a Al lid on Ebay right now...I think it is MUCH less than 700, but it has some damage to the webbing. Probably Ok on the exterior. Just a thought...

[cstreit]

Bill?

Fiberglass less stable than Carbon Fiber? I was of the opposite opinion (not through true scientific reasoning mind you). can you elaborate?

[Bill Verburg]

Chris, Its been years since I dealt w/ f/g lids but way back when I went through 3 f/g ducktails before I found one the would keep its shape pretty close to original after numerous heat cycles. The RS used a steel lid w/ a steel hoop in the duckbill to maintain its topological properties, few if any aftermarket vendors did so. Rear bumpers that are in close proximity to hot mufflers can have the same problem but to a lesser degree because of thinner sections and compound curves. In the case of an engine lid w/ minimal curvature and often thick sections for strength the warping will be worse and be more visible.

I've discussed f/g and carbon fiber/kevlar components over the years w/ various vendors and the techs in the shop that I have an interest(we build large boats and have built a few carbon fiber masts ~80' long, the weight savings are on the order of tons over an equivalent wooden mast). Each material has its strengths and weakness. Carbon fiber is light and dimensionaly stable after heat cycling but is weak in regard to ballistic impacts. So its good for engine lids but not for front bumpers.

[Chuck Moreland]

The rear deck is pretty damn light to begin with. I swapped mine for a FG ducktail and saved about 2 lbs, but added the tail.

Being high and rearward makes it a prime place for removal, but there just isn't much to take away. Much, much more benefit from going to FG bumpers / hood / doors.

[pwd72s]

Originally posted by Chuck Moreland
The rear deck is pretty damn light to begin with. I swapped mine for a FG ducktail and saved about 2 lbs, but added the tail.

Being high and rearward makes it a prime place for removal, but there just isn't much to take away. Much, much more benefit from going to FG bumpers / hood / doors.

Or in my case, religiously obeying weight loss clinic instructions..

[Randy Webb]

"Much, much more benefit from going to FG bumpers / hood / doors. "

- Yup -- but this is a street car. Also, wt. off the rear is more advantageous than off the middle of the car.

[island911]

Originally posted by cstreit
Bill?

Fiberglass less stable than Carbon Fiber? I was of the opposite opinion (not through true scientific reasoning mind you). can you elaborate?

Bill has it, kinda.
Think about wood products, they're like composites. . .
Have you ever noticed how plywood most always has an odd number of alternating plys? This is because wood shrinks and expands differently across the grain, compared to with the grain. If the plywood had the outter plys oriented at 90° from each other, the panel would warp badly with the first change in moisture content.

In composites, you have some guy slapping down layers of say glass, over the cuved mold to make the lid, for instance. What often happens is what's refered to as an unblanced stucture. (like poorly thought out plywood). . .. . Although with composites, the movement in the fiber direction is more from thermal expansion.

Here's where the beauty of CF comes in. Where most materials expand with temp, CF hardly moves at all . . in fact it will shrink just a tiny tiny amount in the fiber direction. Thus, you can have a stable composite structure, even when little thought has been given to the lay-up.

[Bill Verburg]

island911,
Thanks, I knew there was something I was missing. The last Duck was great! The others miserable pieces of c***.